Although not limited thereto, the present invention is particularly adapted for use with integral rocket-ramjet engines for aircraft (e.g., missiles). Such engines comprise a combustion chamber lined with concentric cylinders of a solid ramjet fuel and a solid rocket propellant. Initially, the rocket propellant is ignited and burned without any air passing into the combustion chamber. In this phase of operation, the engine acts as a rocket. After the rocket propellant is burned, air is permitted to flow through the interior of the solid ramjet fuel cylinder which then burns in the presence of air to effect ramjet action.
A persistent problem with ramjet engines of this type is circumferential distortion and uneven burning of the inside wall of the fuel cylinder during ramjet operation. In this respect, the combustion process in a solid fuel ramjet has fuel "rich" and fuel "lean" zones which restrict the attainment of high combustion efficiency. In the past, attempts have been made to improve combustion efficiency with the use of orifice plates and vortex generators at the combustor entrance to induce turbulence; but these devices achieve only marginal improvement and influence only a fraction of the total airflow through the combustor. An air-pass system which promotes total flow mixing in an aft combustor has markedly improved combustion efficiency, but such systems add significant complexity and weight.